In recent years, an automobile (hereinafter, referred to as a “vehicle”) has been developed which generates electricity at the time of braking in order to consider the environment and increase fuel-efficiency. The braking energy generated at the time of braking is recovered as electric energy by use of a regeneration system. This regeneration system charges power (hereinafter, referred to as “regeneration power”) generated from a generator when the vehicle reduces speed. The charged regeneration power is used in running the vehicle except for the reduction of speed. Therefore, it is possible to decrease the generation amount of the generator except for the reduction of speed. As a result, the load on the engine for generating electricity by the generator is decreased, and thereby the fuel-efficiency of the vehicle can be increased. Regeneration power is generated in a large amount for a short period of time at the time of the reduction of speed. The generated regeneration power is recovered to an electricity storage device which charges the power in an electric double layer capacitor via a DC/DC converter. The electric double layer capacitor has good rapid charging/discharging characteristics and thus is suitable for recovering the regeneration power.
When this electricity storage device is mounted in a vehicle, detection and determination of abnormality occurring in the electricity storage device is required to have a high reliability. A device determining abnormality is disclosed in, for example, Patent Citation 1. FIG. 7 is a block diagram illustrating the main part of an abnormality determination unit in a vehicle power diagnosis device in Patent Citation 1.
In FIG. 7, terminal voltage detection unit 103 detecting terminal voltage value Vb of a battery and current detection unit 105 detecting discharging current value Ib of the battery are connected to abnormality determination unit 101. Abnormality determination unit 101 is provided with comparison determination unit 107 and memory unit 109. Of detection results by terminal voltage detection unit 103, terminal voltage signal Vd is transmitted to comparison determination unit 107 and terminal voltage signal Ve is transmitted to memory unit 109. Of the detection results by current detection unit 105, detection current signal Id is transmitted to comparison determination unit 107.
Abnormality determination unit 101 is provided with memory removal unit 111 connected to memory unit 109, and timer 113. Memory removal unit 111 is a switch removing terminal voltage signal Ve stored in memory unit 109. If memory removal unit 111 is turned on at the time of changing a battery, terminal voltage signal Ve is reset to a predetermined value. Timer 113 transmits starting signal Bc to memory unit 109 after elapse of a predetermined time since the ignition SW is turned on.
Next, the operation of abnormality determination unit 101 of the vehicle power diagnosis device will be described. Boundary characteristic C with respect to discharging current value Ib and terminal voltage value Vb of a battery is stored in memory unit 109 in advance. Boundary characteristic C is a characteristic indicating a boundary between normality and abnormality of a battery when discharging current value Ib is expressed on the transverse axis and terminal voltage value Vb is expressed on the longitudinal axis. When discharging current value Ib and terminal voltage value Vb reach the region below boundary characteristic C surrounded by the oblique line, the battery is determined to be abnormal. Terminal voltage signal Vd from the terminal voltage detection unit 103 and detection current signal Id from current detection unit 105 are input to comparison determination unit 107. Characteristic signal Hk based on terminal voltage value Vb and discharging current value Ib from memory unit 109 is input to comparison determination unit 107 together with terminal voltage signal Vd and detection current signal Id. Comparison determination unit 107 compares terminal voltage signal Vd and detection current signal Id with characteristic signal Hk. As a result of the comparison, when terminal voltage signal Vd and detection current signal Id are smaller than characteristic signal Hk and are thereby placed in the region equal to or less than boundary characteristic C, the battery is determined to be abnormal. If the battery is abnormal, comparison determination unit 107 outputs abnormality signal Kc. Based on abnormality signal Kc, an abnormality warning means or the like notifies the driver of the occurrence of the abnormality.
Like the prior art, a battery abnormality can be determined even when the above-described vehicle power diagnosis device is used for a vehicle which does not recover regeneration energy. However, in a vehicle mounted with an electricity storage device using a regeneration system, there are problems as follows.
In the electricity storage device using the regeneration system, an electric double layer capacitor is used as an electricity storage unit. Charging and discharging of this electric double layer capacitor are carried out via the DC/DC converter. When regeneration power is charged in the electricity storage device by this configuration, and when the abnormality is determined in the same manner as the prior art based on the voltage between a positive polarity and a negative polarity of the electricity storage device and a current flowing through them, there is a possibility that it is uncertain whether or not the electricity storage unit is normally charged. That is to say, a portion of a current input to the DC/DC converter flows as a leakage current due to abnormality of the DC/DC converter. In this case, the current flowing to the electricity storage unit lessens, and thereby the charging voltage is lowered. However, if only the voltage between a positive polarity and a negative polarity of the electricity storage device and the current flowing through them are detected, there is a possibility that the electricity storage device lies in a normal range in appearance. As a result, although the DC/DC converter is abnormal, the electricity storage device is probably determined to be normal.    [Patent Citation 1] JP-A-2000-206215